This invention is related to the recovery of hydrocarbons by the use of a polymer containing fluid and more particularly through the use of a Beta-(1.fwdarw.6)-D-glucan linear homopolysaccharide otherwise known as deacetylated pustulan.
Generally, oil or hydrocarbons are recovered from subterranean formations initially employing primary recovery techniques. Once primary production is no longer economically feasible, some form of enhanced recovery is applied to these formations to abstract further quantities of oil. One of the earliest and most popular forms of enhanced oil recovery is water injection in which water or brine is injected into the hydrocarbon containing formation to force the residual hydrocarbons contained therein through the formation to a production well which is placed at a appropriate location. Since the viscosity of the hydrocarbons present in the hydrocarbon bearing formation is usually higher than the viscosity of water or other fluids injected into the formation, the quantity of hydrocarbons removed by such methods is small and further, frequently results in the bypassing of a substantial portion of the hydrocarbons by the less viscous water. This effect is referred to as viscous fingering. This situation is further aggravated by the presence of zones of high permeability at various levels in the hydrocarbon bearing formation. These so called "thief" zones also permit the escape of a substantial portion of the relatively low viscosity water or brine without any displacement of hydrocarbons.
One method of improving the efficiency of enhanced recovery techniques has been through the addition of a substance to the water or brine to increase its viscosity. U.S. Pat. Nos. 2,827,964 and 3,039,529 describe the use of high molecular weight, partially hydrolyzed polyacrylamides as thickening agents for aqueous fluids employed in enhanced oil recovery systems.
U.S. Pat. No. 3,581,824 describes the use of a heteropolysaccharide produced by bacterial fermentation of carbohydrates for this same purpose. U.S. Pat. No. 3,490,533 sets forth increasing the viscosity of the water or brine through an in situ polymerization process wherein a polymerizable monomer and a polymerization catalyst having a latent period of activity are injected into the oil bearing formation to either block areas of high permeability or form high viscosity fluids therein and to aid in the removal of the oil from the oil bearing formations.
Problems have arisen with the use of viscous fluids for enhanced oil recovery due to the expense of their formation and the large energy required for the handling and injection of the viscous fluid into wells, as compared to the injection of water or brine. The high viscosity of previous fluids required the use of higher energies for mixing and pumping. Further, the high viscosity fluids have tended to block the areas closest to the injection well thereby making it more difficult to inject the viscous fluid into the hydrocarbon bearing formation and increased the energy and operating cost of such systems. The use of viscous fluids has also been hampered by the cost and toxicity of the monomers necessary and the difficulty of causing the monomer to polymerize at the desired time and in the desired location.